Unlike automobiles, most agricultural tractors and other off-road equipment have substantially no wheel or cab suspension mechanisms for comforting the ride over rough terrain. To comfort a tractor operator's ride, various seat suspension systems have been devised for providing vertical cushioned movement of an operator's seat. These systems need a large range of available seat travel for accommodating many different operators. The seat suspension system also needs to provide a large range of cushioned seat movement for travel over rough or rugged terrain.
Pressurized oil and/or air cushioned seats have been used in off-road equipment. Such seats are designed as weight and height adjustable seats which provide a large degree of seat travel. In operation, these seats usually sense the weight on the seat and adjust the seat height to midstroke of its vertical travel. This permits use of the full stroke of the suspension during operation over rough terrain.
Although they afford a cushioned ride for the operator, such seats also have drawbacks. When the operator is not on the seat, the seat mechanism will adjust for a light operator and when fluid flow to the seat is interrupted or stopped, the seat sinks or falls to the extreme lowest position of its travel. When the seat sinks to its extreme lowest position, it is in a position much too low to allow for tractor operation and is ergonomically uncomfortable.
A simple solution to this problem would appear to be raising the lowermost suspension position of the seat. Albeit attractive, raising the lowermost suspension position of the seat likewise raises the uppermost travel limit of the seat if the desired range of travel is to be provided. Because such seats are usually contained with a hooded cab enclosure, raising the upward travel limit of the seat may require designing the tractor cab roof with sufficient spacing to prevent an operator from striking his head on the roof of the tractor cab. As may be readily appreciated, extending a tractor cab roof to a height higher than necessary can be a costly proposition. Moreover, raising the lowermost suspension position of the seat may also result in a conflict with S.A.E. standards. That is, S.A.E. sets a prescribed "seat indication point" range which governs how far above the tractor cab flooring the operator seat is to be arranged when the seat is positioned midstroke of its travel. Besides raising the upward travel limit of the seat, raising the lowermost suspension position of the seat would adversely move the midstroke position of the seat beyond the "seat indication point" range prescribed by S.A.E. standards.
Until now, no one has conceived of a simple solution to the problem. That is, no known seat arrangement has been designed in a manner which satisfies all of the above requirements. No known seat arrangement provides a unique combination of a large range of cushioned seat travel within S.A.E. standards and that will not assume a position too low for operation when the fluid flow thereto is interrupted or stopped.